Stack identical uv islands on top of each other
Install blender 2.79 from www.blender.org
Open the preferences and go to the input tab.
Change the pull down menu showing "name" to "key-binding".
Enter the shortcut you used with blender 2.79.
Go to the relevant part of the list ("UV Editor") and look up the name of the function,
which is called by that shortcut.
Remember that function namen. Exit blender 2.79.
Start blender 2.80. 
Enter the preference dialog and select "keymap".
Search for the function name (or a shorter version of its name. If the blender devs
renamed it it will shurely be named similiar. Play with the function name a little
bit.) Find the new short cut.
And finally: Use that shortcut... ;)